This invention relates to a technique of distributing a load among a plurality of servers in a file server or network attached storage (NAS) that is connected to clients via a network and stores data used by the clients.
There has been proposed a NAS in which a storage system connected to a network is used as a shared disk by client computers connected to the network. The NAS is composed of at least one server that contains a network interface and other components, and at least one disk drive that stores data.
To give an example, U.S. Pat. No. 6,671,773 discloses a NAS with a cluster configuration in which a plurality of servers are connected to a network. In a system described in U.S. Pat. No. 6,671,773, network elements, switching elements, and disk elements correspond to servers of the NAS. The system described in U.S. Pat. No. 6,671,773 can have a plurality of network elements that share a file system. The system described in U.S. Pat. No. 6,671,773 also has a plurality of disk elements to migrate data on a disk basis. Each of the network elements can access all file systems that are managed by the disk elements. The migration of a disk storing a file system between disk elements does not prevent each network element from accessing all the file systems.
A network file system (NFS) has been proposed as a type of file system that allows access to files dispersed on a network. According to NFS v4, the latest version of NFS at present (see RFC 3530, “NFS version4”, P. 57-61, IETF Home Page, searched online on Mar. 15, 2006, Internet, URL: http://www.ietforg/home.html), when a file system migrates between servers, the servers notifies a client that attempts to access the file system of information on to where the file system has migrated. Receiving the information, the client accesses the file system at the migration destination by following the notified location information.